GOB Chemistry Study Guide: Carbohydrates, Lipids, and Proteins

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Carbohydrates

Monosaccharides and Disaccharides

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, and are classified based on the number of sugar units present.

Monosaccharides: Simple sugars with a single unit, such as glucose and fructose.
Disaccharides: Composed of two monosaccharide units joined by a glycosidic bond, such as sucrose and lactose.
Hemiacetals: Functional groups formed when an aldehyde reacts with an alcohol within a monosaccharide, leading to ring formation.
α- and β-anomers: Isomers of cyclic monosaccharides differing in the position of the -OH group on the anomeric carbon.

Example: Glucose can exist as α-D-glucose or β-D-glucose depending on the orientation of the hydroxyl group at carbon 1.

Reduction and Reducing Sugars

Monosaccharides can undergo reduction to form sugar alcohols, and some sugars can act as reducing agents.

Reduction: Conversion of the carbonyl group (aldehyde or ketone) to an alcohol.
Reducing sugars: Sugars that can reduce mild oxidizing agents, such as Benedict's reagent, due to a free aldehyde or ketone group.
Nonreducing sugars: Sugars where the anomeric carbon is involved in a glycosidic bond, preventing reduction.

Example: Glucose is a reducing sugar; sucrose is a nonreducing sugar.

Glycosidic Bonds and Polysaccharides

Glycosidic bonds link monosaccharide units in disaccharides and polysaccharides.

Glycosidic linkage: Covalent bond formed between the anomeric carbon of one sugar and a hydroxyl group of another.
Polysaccharides: Long chains of monosaccharide units, such as amylose, amylopectin, and glycogen.
Bonds in polysaccharides: Amylose has α(1→4) linkages; amylopectin and glycogen have both α(1→4) and α(1→6) linkages (branch points).

Example: Glycogen is highly branched, making it more readily mobilized for energy.

Comparison of Polysaccharides

Polysaccharides differ in structure and function.

Polysaccharide	Structure	Function
Amylose	Unbranched, α(1→4) linkages	Energy storage in plants
Amylopectin	Branched, α(1→4) and α(1→6) linkages	Energy storage in plants
Glycogen	Highly branched, α(1→4) and α(1→6) linkages	Energy storage in animals
Cellulose	Unbranched, β(1→4) linkages	Structural support in plants

Additional info: Humans cannot digest cellulose due to lack of enzymes for β(1→4) bonds.

Lipids

Fatty Acids and Triglycerides

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

Saturated fatty acids: No double bonds; higher melting points.
Unsaturated fatty acids: One or more double bonds; lower melting points.
Triglycerides: Esters formed from glycerol and three fatty acids.

Example: Olive oil contains mostly unsaturated fatty acids, while butter contains saturated fatty acids.

Prostaglandins

Prostaglandins are lipid compounds derived from fatty acids that act as local hormones.

Function: Regulate inflammation, pain, and fever.
Production: Synthesized from arachidonic acid; can be blocked by NSAIDs (e.g., aspirin).

Hydrolysis and Saponification

Hydrolysis and saponification are reactions that break down lipids.

Hydrolysis: Reaction with water to break ester bonds, forming fatty acids and glycerol.
Saponification: Hydrolysis of triglycerides with a strong base to produce soap and glycerol.

Equation:

Micelles

Micelles are spherical aggregates of fatty acid salts in water, important for solubilizing lipids.

Structure: Hydrophobic tails inward, hydrophilic heads outward.
Function: Aid in absorption of fats and fat-soluble vitamins.

Complex Lipids

Complex lipids include phospholipids, sphingolipids, glycolipids, and cholesterol.

Phospholipids: Major component of cell membranes; contain phosphate group.
Sphingolipids: Contain sphingosine backbone; important in nerve cell membranes.
Glycolipids: Lipids with carbohydrate groups; involved in cell recognition.
Cholesterol: Steroid; modulates membrane fluidity and is precursor for steroid hormones.

Lipoproteins

Lipoproteins transport lipids in the blood.

Lipoprotein	Function	Origin
Chylomicron	Transport dietary lipids	Intestine
VLDL	Transport triglycerides from liver	Liver
LDL	Deliver cholesterol to tissues	Liver
HDL	Remove excess cholesterol	Liver

Membrane Structure and Transport

Cell membranes are composed of a phospholipid bilayer and proteins, allowing selective transport.

Fluid mosaic model: Membranes are dynamic and flexible.
Transport processes: Simple diffusion, facilitated diffusion, active transport.

Example: Glucose enters cells via facilitated diffusion using a transporter protein.

Amino Acids and Acid-Base Properties

Amino acids can be classified based on the properties of their side chains.

Nonpolar: Hydrophobic side chains (e.g., alanine, valine).
Polar neutral: Uncharged polar side chains (e.g., serine, threonine).
Polar basic: Positively charged side chains (e.g., lysine, arginine).
Polar acidic: Negatively charged side chains (e.g., aspartic acid, glutamic acid).

Additional info: Acidic amino acids have carboxylate groups; basic amino acids have amine groups.

Proteins

Collagen Structure

Collagen is a fibrous protein composed mainly of glycine, proline, and hydroxyproline.

Structure: Triple helix formed by three polypeptide chains.
Vitamin C: Required for hydroxylation of proline and lysine, stabilizing collagen structure.

Protein Structure: Tertiary Structure

Tertiary structure refers to the overall three-dimensional shape of a protein, stabilized by interactions among side chains.

Hydrophobic interactions: Nonpolar side chains cluster away from water.
Hydrophilic interactions: Polar side chains interact with water.
Salt bridges: Ionic bonds between acidic and basic side chains.
Hydrogen bonds: Between polar side chains.
Disulfide bonds: Covalent bonds between cysteine residues.

Hydrolysis and Denaturation

Proteins can be broken down or lose their structure through hydrolysis and denaturation.

Hydrolysis: Cleavage of peptide bonds by water, producing amino acids.
Denaturation: Loss of protein structure due to heat, acids, bases, alcohol, or heavy metals; disrupts non-covalent interactions.

Example: Cooking an egg denatures the proteins, causing them to solidify.